[dev.garbage] lib/codereview: allow hg submit to commit new branch if CL description says so
[dev.garbage] lib/codereview: allow hg submit to commit new branch if CL description says so

This means I won't have to edit the plugin when I create
the next dev branch.

LGTM=r, adg
R=r, adg
CC=golang-codereviews
https://codereview.appspot.com/148950045

bryanxu/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,webfd/go-zh